Treatment such as sewage treatment includes a process of reducing the concentration of a target component in swage water, such as ammonia nitrogen, to a predetermined concentration or less in a biological reactor. In such a process, in order to activate microorganisms, air is sent into the reactor using a blower or the like.
When doing this, if air is continued to be sent even though the concentration of the target component is the predetermined concentration or less, wasted power consumption occurs, and therefore usually, the blower is controlled while successively measuring and monitoring the concentration of the target component contained in the sewage water in the reactor.
As a measurement device used for such successive measurement, for example, as described in Patent Literature 1, one capable of performing successive measurement in a state of being immersed in a reactor without using any reagent, i.e., one using a so-called ion electrode method is suitable.
In such a measurement device, in order to secure measurement accuracy, calibration using a calibration liquid is performed. However, when the calibration liquid itself is a dangerous one or an unstable one, such as a calibration liquid used for ORP measurement or residual chlorine measurement, the problem of the difficulty to prepare the calibration liquid occurs.
Also, when as the measurement device, using a device affected by the interference due to a component (an interfering component) other than the target component, such as a device using an ion electrode method, the effect of the interference due to the interfering component is changed depending on the time-dependent state of a sample, and therefore even when performing the calibration using a calibration liquid, the measurement accuracy is not necessarily high.